1. Field of the Invention
The present invention relates to a control method and apparatus for convergence of a projection television, and more particularly, to a convergence control method and apparatus for a projection television which magnifies images displayed on three cathode ray tubes for the colors red, green, and blue with lenses and projects the images onto a screen. The present application is based on Korean Application No. 2001-55555, filed Sep. 10, 2001, which is incorporated herein by reference.
2. Description of the Related Art
In a projection television, three images from the red, green, and blue cathode ray tubes and lenses are projected onto a screen such that they overlap. The degree to which the images overlap on the screen is expressed by the term xe2x80x9cconvergencexe2x80x9d. A displacement between the three images is called a xe2x80x9cmisconvergencexe2x80x9d. The earth""s magnetic field near the projection television may be a main cause of the misconvergence. The convergence of a projection television can be adjusted at any time.
When a conventional projection television operates in a convergence adjustment mode in response to a user""s command, a normal display mode is interrupted. For example, a user adjusts the convergence of the projection television by manipulating a convergence adjustment button on a remote controller or a user control board attached to a television receiver. This method of convergence adjustment in a projection television is disclosed in U.S. Pat. No. 4,951,131.
The conventional convergence adjustment is conducted by pressing a convergence adjustment button based on a decision made by the user to adjust the convergence and causes the following problems.
First, it is difficult for an inexperienced user to make a correct decision as to when he/she should adjust the convergence, so lower quality pictures may be viewed by the inexperienced user.
Second, it is inconvenient to perform a manual convergence adjustment performed based on a decision made by a user whenever the picture quality is deteriorated due to the earth""s magnetic field.
Third, normal picture display is interrupted for a few seconds or a few minutes while the convergence adjustment is made.
To solve the above-described problems, it is an object of the present invention to provide an automatic convergence control method and apparatus for a projection television, in which a user""s viewing of the projection television is not interrupted for convergence adjustment.
To achieve the object of the present invention, there is provided a convergence control method for a projection television which magnifies images displayed on cathode ray tubes (CRTs) for the colors red, green, and blue with lenses and projects the images onto a screen, the method involving, when a power voltage is applied to the projection television, detecting the start of a synchronization signal of an input image signal. When the start of the synchronization signal of the image signal is detected, a predetermined convergence control pattern signal is generated. Next, the convergence of the projection television is adjusted according to the predetermined convergence control pattern signal. After convergence adjustment is complete, the image signal is displayed.
In the automatic convergence control method according to the present invention, convergence adjustment can be automatically conducted by detecting the start of a synchronization signal of an input image signal. Accordingly, it is unnecessary for a user to adjust the convergence of a projection television while watching the television.
The object of the present invention is also achieved by a convergence control apparatus for a projection television which magnifies images displayed on CRTs for the colors red, green, and blue with lenses and projects the images onto a screen, the apparatus comprising an image signal decoder, a convergence control unit, and a main microcomputer. The image signal decoder processes an input image signal and generates a data signal and horizontal and vertical synchronization signals, and a start signal indicating the start of either the horizontal and vertical synchronization signals. The convergence control unit performs convergence adjustment according to a convergence control command it receives, and generates a completion signal when convergence adjustment is complete. The main microcomputer inputs the convergence control command to the convergence control unit when the start signal is input from the image signal decoder, and performs a control operation to display the image signal when the completion signal is input from the convergence control unit.
In the automatic convergence control apparatus according to the present invention, upon receipt of an image signal, a start signal is generated by the image signal decoder, and a convergence control command is transmitted to the convergence control circuit from the main microcomputer in response to the start signal. Accordingly, there is no need for a user to adjust the convergence of a projection television while watching the television.